Luminescent diode is a semiconductor diode capable of emitting light and serving as a light source. Light-emitting diode (LED) and laser diode are typical examples of luminescent diodes. The advantages of luminescent diodes over traditional light sources include lower energy consumption, longer lifetime, improved robustness, smaller size and faster switching.
Luminescent diode is usually packaged before being incorporated into a circuit. Please refer to FIG. 1, a cross-sectional view illustrating a conventional LED package. The LED package 10 includes a heat-dissipating substrate 102, a conductive layer 103, an insulating layer 104, a package base 105 and a conducting structure 106. The package base 105 is mounted on the insulating layer 104 and has a holding space 1051 supporting a LED chip 101. The conductive layer 103 serves as a positive electrode 1031 and a negative electrode 1031, separated by the insulating layer 104. The conducting structure 106 is formed through the package base 105 and the insulating layer 104 so as to be electrically connected to the conductive layer 103. By wire-bonding the LED chip 101 to the conducting structure 106 via a wire 107, the LED chip 101 can be electrically connected to the positive electrode 1031 and the negative electrode 1032 and receive electricity via external wires 108. An alternative mounting technology, flip chip procedure, can be applied to electrically connect the LED chip 101 to the conducting structure 106 via solder bumps (not shown).
The heat-dissipating substrate 102 includes a heat conductive layer 1021 and an insulating layer 1022. The insulating layer 1022 is made of heat conductive polymer while the heat conductive layer 1021 is usually made of metal material. The insulating layer 1022 interfaced between the heat conductive layer 1021 and the electrodes 1031 and 1032. Such structure makes the heat generated by the LED chip 101 to be dissipated via the heat-dissipating substrate 102. In addition, some conductive adhesive (denoted by “A”) may be applied to an area around the conducting structure 106 between the package base 105 and the conductive layer 103 to firmly fix the package base 105. This increases the area of the heat flow so as to decrease the thermal resistance.
When the LED chip 101 is switched on to emit light, heat is generated along with the light. As shown in FIG. 1, the current flow pathways E and E′ and the heat flow pathway H are too close and thus coupled thermal-electrical effect occurs. The couple effect accelerates the oxidization of the conductive layer 103 and degrades the conductive layer 103 to reduce the conductivity thereof. Furthermore, the degraded conductive layer 103 incurs worse heat dissipation and the accumulated heat affects the luminescence efficiency of the LED chip 101. The efficiency loss further generates more heat. This begins a vicious circle to shorten the lifetime of the LED package 10.
Therefore, there is a need of providing an improved package base of a luminescent diode to obviate the drawbacks encountered from the prior art.